Print hammer control mechanism

ABSTRACT

A printer is provided with a plurality of print hammers, each hammer being maintained in a rest position engaging a deformed elastic body by a hammer control mechanism. The hammer control mechanism includes individual magnetic circuits in combination with a magnetic flux producing element which is provided for selectively maintaining each of the print hammers in the rest position and for selectively releasing print hammers to effect printing. Each magnetic circuit includes a hammer hold portion and a control portion, the hammer hold and control portions being connected in parallel with the magnetic flux producing element. The control portion further includes a permanent magnet and a control coil for effecting release of said hammer from its rest position. Each of the print hammers is released from the rest position by exciting the control coil in the control portion in a first direction to effect a reverse of the polarity of said permanent magnet to thereby decrease the magnetomotive force applied to the print hammer to hold the print hammer in the rest position, the displacement of the print hammer being the product of the release of the energy of the elastic body. The hammer is then returned to a rest position by a return mechanism as the control coil is excited in the opposite direction, the excitation of the coil to return the polarity of the magnet in the control portion resulting in a more responsive hammer control.

United States Patent 1 Gomi [ Sept. 23, 1975 PRINT HAMMER CONTROLMECHANISM [75] Inventor: Yoshifumi Gomi, Matsumoto, Japan [73]Assignees: Kabushiki Kaisha Suwa Seikosha;

Shinshu Seiki Kabushiki Kaisha, both of Tokyo, Japan 22 Filed: Jan. 28,1974 21 Appl. No.: 437,253

[30] Foreign Application Priority Data Primary Examiner-Clifford D.Crowder Assistant ExaminerEdward M. Coven Attorney, Agent, or FirmBlum,Moscovitz, Friedman & Kaplan [57] ABSTRACT A printer is provided with aplurality of print hammers, each hammer being maintained in a restposition engaging a deformed elastic body by a hammer control mechanism.The hammer control mechanism includes individual magnetic circuits incombination with a magnetic flux producing element which is pro videdfor selectively maintaining each of the print hammers in the restposition and for selectively releasing print hammers to effect printing.Each magnetic circuit includes a hammer hold portion and a controlportion, the hammer hold and control portions being connected inparallel with the magnetic flux producing element. The control portionfurther includes a permanent magnet and a control coil for effectingrelease of said hammer from its rest position. Each of the print hammersis released from the rest position by exciting the control coil in thecontrol portion in a first direction to effect a reverse of the polarityof said permanent magnet to thereby decrease the magnetomotive forceapplied to the print hammer to hold the print hammer in the restposition, the displacement of the print hammer being the product of therelease of the energy of the elastic body. The hammer is then returnedto a rest position by a return mechanism as the control coil is excitedin the opposite direction, the excitation of the coil to return thepolarity of the magnet in the control portion resulting in a moreresponsive hammer control.

5 Claims, 5 Drawing Figures US Patent Sept. 23,1975 Sheet 1 0f 23,906,854

FIG. 4

' PRINT HAMMER CONTROL MECHANISM BACKGROUND OF THE INVENTION Thisinvention relates generally to a control mechanism for the print hammersof an on-the-fly printer, and particularly to a control mechanism forsuch print hammers wherein displacement of any individual print hammerhas no influence upon the operation of any other adjacent print hammer.

While the use of printers wherein the print hammers are held in a restposition by a flux producing element and are forced into contact with aprinting surface by a deformed elastic body have taken various forms,embodiments of such printers incorporating a single permanent magnet fora plurality of print hammers have yielded results which are less thancompletely satisfactory. Because the force which is utilized to overcomethe deformed elastic body is the force of a permanent magnet, andbecause it is necessary to reduce the force in order to release thehammer, a change in the reluctance of the portion of the magneticcircuit including the permanent magnet and the print hammer occurs uponthe release of each print hammer.

When the reluctance of a magnetic circuit having a permanent magnet ischanged, the operating point of the permanent magnet for the respectivehammer is changed in order to effect release of same. The change in theoperating point of the permanent magnet, influences the operating pointof the permanent magnet at the adjacent columns and the print hammersassociated therewith which have not yet been released from the hammerrest position. Although coupling a hammer hold circuit and a hammercontrol circuit in parallel to a permanent magnet has been shown to behelpful in reducing the change in the operating point of such permanentmagnets, it has been recognized that the smaller the change in theoperating point of the magnet, the quicker the response speed of thehammer and therefore, the faster printing can be effected. Furthermorehigher response speeds and lower power consumption are the optimumconditions desired in a print hammer control mechanism. Accordingly, itis desired to provide a print hammer control mechanism which has higherresponse speed yet utilizes a minimum of power.

SUMMARY OF THE INVENTION Generally speaking, in accordance with theinvention, a printer is provided having a plurality of print I hammersdisplaceable between a rest position and a print position, an elasticbody maintained in a deformed state by each of said print hammers at itsrest position, and a magnetic circuit control means associated with eachof said columns for selectively holding each said print hammer at itsrest position and releasing same for displacement to a print position.The magnetic circuit control means includes a magnetic flux producingelement common to at least two of said columns, and a first hammer holdmagnetic circuit portion associated with each print hammer including aportion associated with each print hammer including a release coil and apermanent magnet associated therewith, the release coil including meansfor applying signals thereto. The first and second magnetic circuitportions are connected in parallel with the magnetic flux producingelement, each of the magnetic circuit control means being adapted tohold the respective hammers in a rest position and to release therespective hammers on application of a signal to its control coil meansby means of said signal applying means in a first direction so as toreverse the polarity of the permanent magnet and thereby decrease themagnetomotive force applied to same hammer. the energy stored in therespective deformed body displacing said respective hammer from saidrest position to said print position upon said decrease in saidmagnetomotive force. A mechanism for returning the respective hammer toa rest position is provided, the coil signal applying means applying asecond signal to the coil to thereby return the permanent magnet to itsoriginal polarity coincident with the return of the hammer, to effect animproved hammer control.

Accordingly, it is an object of this invention to provide an improvedprint hammer control mechanism wherein a hammer is held at a restposition by the magnetic force generated by a magnetic flux producingelement while storing energy in an elastic body such as a spring.

Another object of the invention is to provide an improved hammer controlmechanism for a printer which may be actuated by relatively smallcontrol current to thereby effect small power consumption.

Still another object of the invention is to provide a printer having aplurality of hammers controlled by a common magnetic flux producingelement and individual column circuit control devices wherein theoperation of one of said hammers does not affect operation of any of theadjacent hammers.

Still a further object of the invention is a printer having a pluralityof hammers controlled by individual column circuit control deviceswherein a high response speed is effected by utilizing a minimum ofpower.

Still another object of the invention is to provide a printer and aplurality of hammers controlled by a single flux producing elementcommon to each of the hammers, and individual column magnetic circuitcontrol devices each including a permanent magnet.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combination of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of theinvention, reference is had to the following description taken inconnection with the accompanying drawings in which:

FIG. I is a partially sectioned side elevational view of the operativeportion of one column of a printer constructed in accordance with theprior art;

FIGS. 2 and 3 are partially sectioned side elevational views of theoperative portion of one column of a printer including an improvedhammer control mechanism constructed in accordance with the instantinvention;

FIG. 4 is a graphical representation of a hysteresis loop of the controlpermanent magnet utilized in the embodiment depicted in FIGS. 2 and 3;and

FIG. 5 is a side elevational view of a second embodiment of an operativeportion of one column of a printer including an improved hammer controlmechanism constructed in accordance with theinstant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, onecolumn of a multicolumn printer constructed in accordance with prior artis depicted. The printer includes a hammer I mounted for longitudinaldisplacement on suspending springs 2. A magnetic circuit for the controlof the displacement of the hammer is provided having a first portionconsisting of yokes 3 and 4 for holding hammer l in a rest position bymeans of a magnetic field caused by fluit from a permanent magnet 6 anddepictcd as loop i. A second portion of the magnetic circuit illustratedby loop ii is formed by permanent magnet 6, yoke 3, yoke 4, anadditional yoke 5, and a control coil 8 wound about yoke 5. The rear endof hammer 1 is disposed in contact with transmitting lever 9, whichlever is pivoted about pivot 9' and which lever further engages anddeforms drive spring 10 when the hammer is in the rest position asillustrated in FIG. 1. The stroke of transmitting lever 9 is limited bya stopper 12 which is struck by said lever before the hammer strikesrecording paper and inked ribbon 14 against print drum 13. Reset cam 11is provided for returning the print hammer and spring to a rest positionafter the hammer is operated and the printing is completed by rotatingcam 11 against the lower portion of the transmitting lever 9 to therebydeform the spring into the rest position. Printing is effected byengagement of the front end of the hammer 1 against the recording paper15 to force the recording paper against the ink ribbon 1 4 and thesurface of a character-carrying drum 13. Drum 13 is continuouslyrotating and has a series of characters circumferentially spaced inalignment with the column represented by FIG. 1. In practice, one suchcircumferential arrary of characters will be provided for each column ofthe printer. The characters may consist of the symbols, numbers orletters desired.

The operation of the prior art arrangement depicted in FIG. 1 isunderstood by making reference thereto wherein the hammer is depicted ata rest position. At this'position hammer l is held by yokes 3 and 4 dueto the holding force generated by the flux loop 1' which includes thehammer, yokes 3 and 4 and permanent magnet 6. The holding force appliedto hammer l is sufficient to overcome the driving force of drive spring10 and is further sufficient to hold the hammer in position despite theinfluence of changes in temperature, vibration and the like. Ashereinabove noted, a second loop ii is formed, including permanentmagnet 6, and is con nected in parallel with the first loop 1' throughpermanent magnet 6. As noted above, a character carrying drum 13 rotatesat a predetermined speed. When the selected character approachesalignment with hammer l, a signal is applied to control coil 8. Thedirection of the signal appliedto the control coil 8 is such as toincrease the quantity of magnetic flux flowing in magnetic flux loop ii.When the magnetic flux in loop ii is increased, the flux in loop ibetween the points A and B is decreased, thus decreasing the holdingforce on the hammer, allowing the holding force to be overcome by theforce of drive spring 10 acting upon the hammer. The print hammer isdriven in the direction of the character on the print drum by the springand continues to be supplied with energy until transmitting lever 9 isbrought into contact with stopper 12. If the print hammer strikesagainst the character drum the printing function is performed. The printhammer rebounds off the print drum and is returned to the rest position,spring 10 being returned to the rest position by reset cam 11.

It is noted that the operation of the prior art hammer is less thancompletely satisfactory in view of the following. When the hammer isreleased from its hammer hold position, the operating point of thepermanent magnet is changed. Alteration of the operating point of thepermanent magnet affects the adjacent columns which have hammer controlmagnetic circuits cooperating with the same permanent magnet, thehammers of which have not yet been released from their respective hammerhold positions. The change in operating point of the permanent magnet atthe released hammer column increases the amount of magnetic flux flowingto the hammer hold portion of the magnetic circuits of the adjacentcolumns which have not yet been released. This increase in the amount offlux in the adjacent columns causes an increase in the force of loop 1'in the other columns and a stronger signal must then be applied to thecontrol coils in the adjacent columns in order to allow the hammers ofsuch adjacent columns to be released. Moreover, even if the power issufficient to release the hammer of the adjacent columns, an increase intime is required to supply the current needed for releasing suchadjacent hammers. Variations in the time between the application of aprint command and the release of associated hammer depending on whetheranother hammer has previously been released results in a reduction inprinting efficiency, and hence a reduction in the response time of suchprinting.

Reference is now made to FIGS. 2 and 3 wherein a printer controlmechanism for eliminating the abovementioned defects is depicted. Aprint hammer 21 is depicted in FIG. 2 in a rest position where it isheld thereby by a hammer hold magnetic circuit consisting of yokes 23and 24 having attractive faces 23a and 24a respectively for holdinghammer 21 in a rest position, as illustrated in FIG. 2, by means of themagnetic field caused by the flux from a permanent magnet 26 anddepicted as loop iii. A hammer control circuit is illustrated by loop vand is formed by permanent magnet 26, a portion of yoke 24, a portion ofyoke 23, a control permanent magnet 27, coil core 25, and a control coil28 wound about coil core 25, control permanent magnet 27 and yoke 23.Both the hammer hold circuit illustrated as loop iii, and the magneticcontrol circuit illustrated as loop v are connected in parallel withpermanent magnet 26 for holding the hammer and releasing same in thesame manner as depicted in FIG. 1. The control permanent magnet 27 isselected so that when the hammer is in a rest position, the polaritiesof the control permanent magnet 27 and the permanent magnet 26 face eachother in the manner depicted in FIG. 2.

In operation, the hammer remains at a rest position, as depicted in FIG.2. When the selected character on a character carrying drum (not shown)approaches a position opposite the print hammer 21, the control coil 28is excited in a first direction so as to reverse the direction in thepolarity of the control permanent magnet 27 and change the polarity ofthe control permanent magnet thereby reducing the magnetomotive forcebe- 27 and the permanent magnet 26 have opposite ,polarities facing eachother. The amount of magnetic flux flowing to thehammer hold circuitdepicted by .mag-

netic flux loop vii isdecreased rapidly. Uponcomple tion of the printingaction by the print hammer, the

print hammer is returned by action of a cam in the,

same manner illustrated in FIG. I. Coincident with the return of thehammer the control coil 28 is excited in a second direction in order toreverse the polarities of the control permanent magnet 27 and returnsame to its rest position polarities so that the same polarities in thepermanent magnet 26 and the control permanent magnet 27 again face eachother.

Reference is now made to FIG. 4 wherein a hysteresis loop of the controlpermanent magnet 27 provided in a control magnetic circuit is depicted.When print hammer 21 is held in a hammer rest position, the operatingpoint of the control permanent magnet 27 is at a point a. When thecontrol coil 28 is energized to effect a release of the hammer, theoperating point of the permanent manget is moved from point a to pointb. It is noted that the f point of the hysteresis loop is the point atwhich the control permanent magnet 27 is rapidly reversed and since thepoint a is so close thereto, a small application of current to thecontrol coil will affect an immediate and rapid reversal of polaritiesin the control permanent magnet. As explained above, upon excitation ofcoil 28, flux loop iii is also reduced and the print hammer is releasedfrom its rest position. It is appreciated that by providing such a rapidchange of polarities of permanent magnet 27, a more rapid response iseffected when the excitation coil 28 is energized.

When control coil 28 ceases to be energized, the operating point of thecontrol permanent magnet is moved to point c on the hysteresis loop. Atthat point, magnetic flux is flowing through the magnetic flux loop videpicted in FIG., 3. Accordingly, by selecting point c in the hysteresisloop at a proper position, it is possible to eliminate the defectdescribed with respect to a hammer mechanism'shown in FIG. 1, namely,that the operation time of the hammer is altered when the hammer isoperated because the hold force for the print hammers in the adjacentcolumns not having been released is increased.

Upon completing the printing action, the print hammer is returned to itsrest position in the usual manner. Coincident therewith, the polarity ofthe control permanent magnet is returned to the direction depicted inFIG. 2, by applying a signal of a second direction to control coil 28.Upon the return of the polarity of control permanent magnet 27 theoperating point thereof is moved along the hysteresis loop from points0, to d, to e. Upon termination of excitation in that direction, theoperating point of the control permanent magnet is returned from point eto point a and the hammer mechanism is returned to the rest positiondepicted in FIG. 2 Accordingly, the magnetic flux produced from thepermanent magnet 26 does not separately flow through the magnetic loop1' and ii at the time the hammer is attracted such as the conventionalhammer mechanism depicted in FIG. 1. Moreover, since the magnetic fluxfrom the permanent magnet 26 can be minimized a small magnet for holdingthe hammers will become particularly adapted for such use. Further, theresponse time as well as a decrease inthe power consumed thereby will beeffected and, the effect of operating hammers on adjacent columns willbe eliminated.

Reference is now made to FIG. 5,wherein a hammer controlmechanismforcontrolling the release of hammer 31 is depicted. A yoke 33 includingan electromagnet 36 wound therearound, and having hammer attracticefaces 33a and 33b to definea hammer hold, circuit while maintaininghammer 31 at a rest position. core 35 includes a control permanentmagnet 37 therein, and a control coil 38 wound therearound. Itisunderstood, that the only differences between the hammer controlmechanism depicted in FIG. 5 and the one depicted in FIG. 2 is thatpermanent magnet 4 maintaining the hammer in a rest position is replacedby an electromagnet formed by yoke 33 and coil 36, the operation beingthe same as the mechanism described above, and providing the sameimproved response time during operation.

It will thus be seen that the objects set forth above, amont those madeapparent from the preceding description are efficiently attained and,since certain changes may be made in the above construction withoutdeparting from the spirit and scope of the invention, it is intendedthat all matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense. i

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetwecn.

What is claimed is:

1. In a printer, respective hammer control means for print hammers whichare arranged in a plurality of columns and each of which is displaceablebetween a rest position and a print position, and having respectivedeformable elastic bodies maintained in deformed condition by theassociated print hammers in the rest position, improved magnetic circuitcontrol means comprising holding means for holding each said printhammer at said rest position, releasing means for selectively displacingsaid print hammer to said print position, and means for producing amagnetic flux, a first hammer hold magnetic circuit associated with eachprint hammer including a portion of the associated print hammer and asecond control magnetic circuit associated with each print hammerincluding a control permanent magnet and control coil means, saidcontrol coil means including means for applying a pulse thereto, saidfirst magnetic circuit and second magnetic circuit being connected inparallel with said magnetic flux producing means, each of said magneticcircuit control means being adapted to hold said respective hammers insaid rest position and to release said respective hammers uponapplication of a pulse to the control coil means by means of said signalapplying means in a direction so as to reverse the polarity of saidcontrol permanent magnet and thereby decrease the magnetomotive forceapplied to said hammer, the energy stored in the respective deformedbody displacing said respective hammer from said rest position to saidprint position upon said decrease in said magnetomotive force.

4. In a printer as claimed in claim 2, and including means for returningsaid print hammer to a rest position upon completion of said printingoperation.

5. A printer as claimed in claim 4, wherein said coil means includes asingle excitation coil. and said means I for applying said firstmentioned pulse to said excitation coil is further adapted to supply afurther pulse of an opposite direction to said excitation coil toreverse the polarity of said control permanent magnet coinci-' dent withthe return of said print hammer to said rest position

1. In a printer, respective hammer control means for print hammers which are arranged in a plurality of columns and each of which is displaceable between a rest position and a print position, and having respective deformable elastic bodies maintained in deformed condition by the associated print hammers in the rest position, improved magnetic circuit control means comprising holding means for holding each said print hammer at said rest position, releasing means for selectively displacing said print hammer to said print position, and means for producing a magnetic flux, a first hammer hold magnetic circuit associated with each print hammer including a portion of the associated print hammer and a second control magnetic circuit associated with each print hammer including a control permanent magnet and control coil means, said control coil means including means for applying a pulse thereto, said first magnetic circuit and second magnetic circuit being connected in parallel with said magnetic flux producing means, each of said magnetic circuit control means being adapted to hold said respective hammers in said rest position and to release said respective hammers upon application of a pulse to the control coil means by means of said signal applying means in a direction so as to reverse the polarity of said control permanent magnet and thereby decrease the magnetomotive force applied to said hammer, the energy stored in the respective deformed body displacing said respective hammer from said rest position to said print position upon said decrease in said magnetomotive force.
 2. In a printer as claimed in claim 1, wherein said means for producing a magnetic flux is a permanent magnet.
 3. In a printer as claimed in claim 2, wherein said permanent magnet and said control permanent magnet have like polarities coupled to each other when said hammer is in said rest position, and upon application of said control release pulse to said control coil means, the polarities of said control permanent magnet being reversed so as to couple the opposite polarities of said permanent magnet to opposite polarities of said control permanent magnet.
 4. In a printer as claimed in claim 2, and including means for returning said print hammer to a rest position upon completion of said printing operation.
 5. A printer as claimed in claim 4, wherein said coil means includes a single excitation coil, and said means for applying said first mentioned pulse to said excitation coil is further adapted to supply a further pulse of an opposite direction to said excitation coil to reverse the polarity of said control permanent magnet coincident with the return of said print hammer to said rest position. 